There are many applications requiring that a process fluid be controllably transferred across an interface between a stationary component and a rotatable component in rotating equipment having at least one component which is rotatable with respect to at least one other adjacent component. Depending upon whether or not the transferred process fluid is at higher or lower pressure than the surroundings, this fluid transfer involves some process fluid leakage or ingestion. Minimizing the process fluid loss or ingestion is important for maintaining rotating equipment performance. As used herein, the term “process fluid” refers to any fluid that is used as the primary working fluid in a device, system, or process.
Minimizing process fluid leakage or ingestion requires a seal between the stationary and rotating components. The sealing function should be accomplished with minimum generation of heat, so that adjacent components and the process fluid itself are not excessively heated. This is particularly important in high speed rotating equipment, where seal rubbing can produce high heat generation. In addition, depending upon the application, the seal arrangement used may have differing pressures acting on the surfaces involved, and the forces produced by these pressures on the seal components need to be managed to insure high loads are not transmitted between the stationary and rotating components. Mechanical seals such as labyrinth seals, brush seals, and finger seals have been used to facilitate such process fluid (air) transfer. However, these mechanical seals may themselves leak and generate excessive heat. Journal type seals have been used for low speed, liquid transfer applications, but may also result in high leakage rates and require close clearance dimensional controls.
The transfer of cooling air (a process fluid) from a stationary tangential on-board injector (TOBI) to the rotating turbine of a gas turbine engine is one example of such an application where conventional mechanical seals have not adequately reduced process fluid leakage or ingestion. The TOBI provides cooling air to the turbine of the gas turbine engine. In particular, an inlet of the TOBI receives air from a compressor of the gas turbine engine or another source of cooling air and passes it through nozzles that impart a swirling moment and direct the discharging stream tangentially to the rotating turbine. The cooling air discharged from the TOBI is delivered into a cavity upstream of the turbine. The cavity may be sealed off by conventional inner and outer mechanical seals that substantially seal the interface between the rotating and stationary (i.e., non-rotating) structures. Unfortunately, some of the cooling air discharged from the TOBI is leaked through the seals, resulting in an adverse effect on TOBI performance. More specifically, leakage of the cooling air from the TOBI results in less cooling air going to the turbine for cooling, thereby causing the turbine to run hotter and shortening its life. If extra cooling air is supplied to compensate for leakage to preserve turbine life, engine performance including fuel consumption and power may be compromised. Other applications requiring that a process fluid be controllably transferred across an interface between a stationary component and a rotatable component in rotating equipment are similarly adversely affected by process fluid leakage or ingestion that is not adequately prevented by conventional mechanical seals.
Accordingly, it is desirable to provide fluid transfer seal assemblies, fluid transfer systems, and methods for transferring process fluid between stationary and rotating components using the same. It is also desired to provide fluid transfer seal assemblies that minimize process fluid leakage and ingestion, heat generation, and manage differing pressure loads that may exist on the sealing components to substantially prevent overload and rubbing.